Process for the cold forming of metal



Dec. 29, 1970 c. McMAsTER 3,550,417

PROCESS FOR THE cow FORMING OF METAL Filed March 14, 1968 3 Sheets-Sheet1 YNVENTOR. ROBERT C. McMASTER QMQMW ATTORNEY Dec. 29, 1970 R. C. MMASTER PROCESS FOR THE COLD FORMING OF METAL Filed March 14, 1968 \Y\\W\ \\R ski ANDRAL SIZING DIE 3 Sheets-Sheet 2 DIE MANDRAL F! G. 2 d

INVENTOR C. MCMASTER *WAQM ATTORNEY ROBERT R. C. M MASTER PROCESS FORTHE COLD FORMING OF METAL Dec. 29, 1970 3 Sheets-Sheet 3 Filed March 14,1968 INVENTOR. ROBERT C. McMASTER mmmmkw sssu1s United States Patent"ice PROCESS FOR THE COLD FORMING 0F METAL Robert C. McMaster, Columbus,Ohio, assignor to The Ohio State University, Columbus, Ohio, aninstitution of higher learning Filed Mar. 14, 1968, Ser. No. 713,036Int. Cl. B21c 37/00 11.5. CI. 72--57 17 Claims ABSTRACT OF THEDISCLOSURE This invention is a system using sonic power to facilitatethe cold rolling and deformation of metals. Sonic vibratory energyintroduced into the work material is transmitted through the materialcausing dynamic stresses in the material. The dynamic stresses enablethe material to be cold-formed at static loadings much lower than thosenecessary in conventional cold-forming operations.

CROSS REFERENCES There is disclosed in patent application, Ser. No.571,490, now Pat. No. 3,396,285 for Electromechanical Transducer by H.M. Minchenko, a transducer capable of delivering extremely high power,i.e., measurable in horsepower (or kilowatts) at an acoustical frequencyrange. The principle underlying the high power output is in thestructural arrangement of the components immediately associated with thepiezoelectric driving elements. In theory and practice, thepiezoelectric elements are under radial and axial pressure that assurethat they do not operate in tension even under intense sonic action.Significantly, the structural design of this transducer, that permitsthe extraordinary power output from the driving elements, resides in thenovel method of clamping the piezoelectric elements both radially andlongitudinally (axially). In this way the acoustic stresses in thepiezoelectric elements are always compressive, never tensile, even undermaximum voltage excitation.

The transducer disclosed in the aforementioned patent application isintended, and therefore utilized, to deliver a steady-state vibratorypower output signal. That is, the piezoelectric assembly is a componentof a resonant structure that will produce a mechanical vibratory outputat the frequency of the driving electrical signaland vice versa.

BACKGROUND In the sonic and ultransonic metal deformation systemsdisclosed in the prior art, sonic and ultransonic vibrations areintroduced through the rolls, dies, press elements, pierces and otherelements commonly used for application of static forces and pressures tothe surface of the work materials. In general, such systems were noteffective for purposes other than some reduction in friction at theinterface with the work material. The effort to vibrate the masses ofrolls, dies, and other force application elements required extremelyhigh vibratory forces to overcome the inertial forces (F ma) of theseelements. Very high levels of sonic power cannot be introduced into workmaterials by this means since the vibration lifts the forming elementout of contact with the work material unless very high static forces(exceedingthe magnitude of the vibratory force) are superimposed. Thelatter condition eliminates the minor advantages of reduction offriction. Tools, dies, rolls, and other force application elements ofthis type tend to fail rapidly in fatigue.

Where longitudinal deformation is desired, and deforming force isapplied transversely, as by rolls, dies, etc., the benefits of applyinglongitudinal vibratory force 3,550,417 Patented Dec. 29, 1970 directlyto the work material in the region where deformation is occurring arelost.

SUMMARY OF INVENTION In the system of the present invention thevibratory energy is applied directly to the work material, and need notvibrate any elements of the forming machinery at all. Very highvibratory stress levels (approaching the elastic limit of the workmaterial) can be applied effectively by this process, without anylimitations related to the ability of the processing machinery towithstand vibratory forces or accelerations.

The cold rolling and forming systems of the present invention differradically from prior art. This invention substitutes dynamic force froma sonic motor for a very large portion of the static forces normallyrequired. The vibratory energy from the transducer produces dynamicstresses which approach the elastic limit of the material but do notexceed it. Static force is applied by the rolls whereby the elasticlimit is exceeded locally and the material is deformed. In conventionalprocesses metallic materials are deformed by static forces producingstatic stresses exceeding the elastic limits of the work materials. Therole of the static force system in the present process is reduced tothat of a control-signal system, and the basic work of metal deformationis done by means of the dynamic vibrational stress waves caused by oneor more sonic power transducers. In consequence, it is estimated thatthe static force requirements could be reduced in ratios of 10:1 to :1or more, as compared with conventional static force deformation systems.

OBJECTS The present invention has as its principal object a method forcold forming steels, aluminum alloys, titanium alloys, and all othermaterials possessing a stress-strain curve with an elastic regionfollowed by a region of plastic deformation.

Another object of the invention is to provide a method of cold formingby which the cold forming of the material may be completed in onecontinuous operation eliminating the necessity for annealing.

Another object of the invention is to eliminate static shear-strainenergy stored in the cold worked material so as to reduce or eliminateruptures and fractures in the work material.

Another object of the invention is to facilitate the cold working ofmetals and alloys by eliminating the necessity for annealing to restoreductility of the material.

Another object of the invention is to provide a method for workingmaterials not normally considered coldformable.

Another object of the invention is to reduce the weight, size, and costof machinery required to perform a given forming operation.

Still another object of the invention is to increase the capabilities ofexisting cold-forming machinery to by ratios of 10:1 to 100:1 or more.

Other objects and features of the present invention will become aparentfrom a reading of the following detailed description when taken inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic View of arolling mill for shaping or reducing the cross-section of metals,alloys, and other plastically-deformable materials by cold rollingutilizing dynamic stresses created by vibratory energy transmittedthrough the work material;

FIG. 2a is a sechematic view of a system for bending metal stookutilizing dynamic stresses created by vibratory-mechanical energytransmitted through the work material; I i w FIG. 2b is a schematic viewof a system for piercing billets to make tubes utilizing dynamicstresses created by vibratory-mechanical energy transmitted through thework material;

FIG. 20 is a schematic view of a system for drawing Wire utilizingdynamic stresses created by vibratory-mechanical energy transmittedthrough the work material;

FIG. 2d is a sechematic view of a system for sizing material using afloating mandral and die in conjunction with dynamic stresses created byvibratory-mechanical energy transmitted through the work material;

FIG. 3a illustrates the sinusoidal dynamic stress wave created by thevibratory energy introduced into the material; the dynamic (sinusoidal)stress waves do not exceed the elastic limits of the material where theenergy is efiiciently transmitted through the material;

FIG. 3b illustrates a dynamic (sinusoidal) stress superimposed on astatic bias stress (tension) which causes the tension elastic limit tobe exceeded once each cycle, causing incremental permanent deformationsin the \work material;

FIG. 3c illustrates the same phenomenon illustrated in FIG. 3b exceptthat the static loading here causes a negative (compressive) stress withthe superimposed dynamic stress causing the negative elastic limit to beexceeded, causing incremental permanent deformations;

FIG. 4a illustrates a typical stress-strain curve for metals havingregions of elastic deformation and plastic deformation; and

FIG. 4b illustrates the progression of incremental deformations withbiased sonic stress applications.

DESCRIPTION OF PREFERRED EMBODIMENT In accordance with the generalconcepts of the present invention the sonic cold forming process of thepresent invention utilizes sonic stress waves directed longitudinallyalong the work material where elongation deformation of the workmaterial is desired. Thus, this longitudinal vibratory stress acts toproduce elongation deformation directly. More particularly, staticforces or pressures applied through rolls, press 'dies, pieces, andother elements tend to be transverse to the elongation direction, butproduce a component of force in the elongation direction. This componentof the applied static force is a major factor in determining thedirections, rate, and extent of elongation deformation in conventionalprocesses. It is also this component of the transversely-applied staticcontrol-signal (bias) force that adds to the longitudinal dynamic forceto guide elongation deformation in the sonic rolling and deformationsystem.

Referring now generally to FIGS. 1 and 2a, a sonic motor 1 or transducer1' is coupled (directly by threads or clamps, or indirectly by means ofimpact either by the output shaft of the sonic motor or by means of anintermediate bouncing-mass element) to the work material to be rolled ordeformed..The sonic vibratory power is introduced to the work material2, such as metallic bar, tube, pipe, sheet, plate, slab, billet, round,ingot, or other length of material, at one end', by the sonic powertransducer 1. Vibratory stress waves pass along this piece of workmaterial from the transducer to the point of application of force orpressure by 'rneans'of rolls, hammers, mandrels, pierces, or otherdevices well-known in metal-working industries for the cold forming ofmetallic materials.

At the rolls 4, 4a, the pointof application of static forces orpressures, the sonic vibratory stresses thus created are added to thelongitudinal components of stress provided by therolls, forging hammer,or other means of applying static forces to createstatic stresses in thework material. Referringto FIGS. 3b and 3c, the sum of the static force(which itself will be of much smaller magnitude than the force requiredfor deformation in processes using only static force) and the dynamicvibratory force passing longitudinally along the work material 2 exceedsthe elastic limit of the work material. With total stresses exceedingthe elastic limit of the material, plastic deformation occurs and themetallic material is readily changed in shape or dimensions. This actionoccurs only in the region where the static force applied by the rolls 4,4a and the dynamic forces create stresses which, when superimposed,exceed the elastic limit of the material.

FIG. 1 illustrates a sonic transducer I mounted at the node 5 to abracket 5a, coupled to work material 2 at the end of the output shaft 3by one of several possible methods mentioned hereinabove. Sonicvibratory power introduced into the work material 2, which may assumeany given geometry (bar, tube, pipe, sheet, plate, slab, billet, round,ingot, etc.), causes vibratory stress waves to pass along the workmaterial 2 from the point of transducer 3 to the point of application offorce by the work rolls 4 or other devices used for metal working(hammers, pierces, mandrels, etc.). The application of static force F atthe node 5 of the transducer feeds the work material 2 into the workingdevices 4 in direction 8 where the static bias force F in FIG. 1 or thecombination of static forces F F and F on the rolls 4a in FIG. 2a causesthe material to deform. The static forces required to deform the workmaterial 2 which has been excited by vibratory-mechanical energy areless by a factor of 10 to 100 than the static forces required to deformwork material 2 which has not been excited by vibratory-mechanicalenergy.

FIG. 2a illustrates the work material 2 being stressed in compression at6 and in tension at 7. Whether the stress introduced into the workmaterial 2 is tensile or compressive the static force required to deformthe material is reduced by a factor of 10 to 100. FIG. 3a illustratesthe stress-time or stress distance relation 9 resulting from the sonicvibratory-mechanical energy introduced into the work material 2. Thedynamic stresses introduced into the work material 2 by the sonicvibratory energy from the sonic transducer 1 may not exceed the elasticlimits 10, 11 of the work material 12 into which they are introduced ifthe vibratory-mechanical energy is to be efiiciently transmitted. FIG.3b illustrates the effect of a static bias force applied to the materialthrough the work rolls 4, 4a resulting in a corresponding static biastensile stress 0 to which the dynamic stress 9 introduced by the sonictransducer 1 is additive. The cross-hatched areas 12 of FIG. 3b indicatethe periods of time which the work material 2 experiences total stress(from the sum of the static 0' and the dynamic stress 9) in excess ofits elastic limit 10 in the tensile direction. During each period inwhich the elastic limit 10 is exceeded by the sum of the static biasincremental deformation adds to the total permanent deformation or set20. As time of application of vibratory'and static stressing continues,the work material follows the static stress-strain curve, FIG. 4b, curvethrough its plastic deformation region 16 until any desired level ofcold deformation (within the capabilities of the work material) havebeen achieved. Thus, it is essential for this process (as for all othercold forming processes) that the material have a plastic range 16 (acurved portion of the stress-strain curve between the elastic limit andthe ultimate tensile-strength at which the material fails or ruptures).

Where the static bias load causes a compressive static stress to beintroduced into the work material 2, the sum of this compressive stressand the dynamic stresses introduced by the transducer 1 will produceincremental deformations 19 in a manner analogous to that describedhereinabove in conjunction with FIG. 3b. FIG. 3c is the graphicalillustration of how a' compressive static stress 1 combines with thedynamic stress to exceed the elastic limit 11 in the negative directionto produce incremental deformation. This compressive deformation 13occurs in a manner analogous to that described hereinabove for thetensile stress in FIG. 3b.

The dynamic stresses 9 combine with tensile or compressive 0' stresseswherever they maybe found in the work material 2. FIG. 2a illustratesthe bending of the work material 2' for which a combination of staticloading producing tensile stresses at point 6 and compressive stressesat point 7 within the work material 2 must be used. The dynamic stresses9 introduced by transducer 1 effectively combine with the stresses atpoints 6 and 7 to exceed the respective elastic limits 10, 11, of thework material 2 producing incremental deformation 12, 13, 19 when thetensile and compressive at points 6 and 7, respectively, are exceeded.

Basically, sonic forming of metals (in particular, cold rolling) may becarried out on any metal possessing stressstrain characteristicsincluding a non-linear region of any type; a typical stress-strain curveis illustrated in FIG. 4a. Such stress-strain curves are characterizedby a linear region 17 (denoting elastic deformation) terminating at theelastic limit 14 and 15 of the material. Beyond the elastic limit 14 and15, the stress-strain curve is deflected; in this area called theplastic region 16, plastic deformation occurs. Plastic deformation isessential to cold forming because the work material 2 once plasticallydeformed, retains a permanent deformation or set. A .workmaterial 2stressed to a value not exceeding the elastic limit 14 and 15, returnsto its original geometry once the stress is removed.

FIG. 4b illustrates how fully-reversed or sinusoidal stresses causesmall plastic deformations 19 or incremental movements along the plasticdeformation region 16 of the stress-strain curve. (Note, however, that asinusoidal wave shape is not the only feasible shape. All other waveshapes with peak values high enough can be used.) A small deformationoccurs with each cycle of vibratory energy introduced into the workmaterial 2 by the transducer 1. The cross-hatched areas 12and 13 ofFIGS.'3b and 3c illustrate the cyclic nature (described hereinabove) ofthe deformations19 which follow the plastic range 16 of thestress-strain curve in FIG. 4b. The lines parallel to the elastic range17 of the stress-strain curve indicate each incremental deformation. 19produced by the-sum of the dynamic sonic stresses 9 (introduced duringeach cycle of sonic vibratory energy) and "static stresses 0' and 0' Theincremental deformations 19 are separated by intervals of releasedstress (typically reversed to a level not exceeding the opposite elasticlimit 15). The reversed stress has the desirable effect of relievingshear strain energy and preventing static shear strain energy from beingbuilt up and stored in the work material .2 as the successive smalldeformations add up to a large total or composite deformation. In fact,the total energy stored or remaining in the material after working isequal to the cross-hatched area 18 of FIG. 4b. Energy equal to theentire area under the stress-strain curve, above the abscissa, andbounded by and including increment 18 of FIG. 4b remains in a materialwhen the material is worked by conventional metal-working processesemploying only static forces to deform the work material 2.

Static shear strain energy is not stored in the workpiece. Such storageof static shear strain energy in work materials deformed continuously bystatic forces (which are maintained by friction with tools, rolls, dies,etc.) can lead to ruptures and fractures of the work material, if

the deformation is carried to high levels. Such ruptures and fracturesdo not appear to occur in the sonic cold forming process. Thus, muchgreater total deformations can be performed without fracture of the workmaterials in the vibratory-mechanical energy or sonic cold workingprocess. The result is that materials not normally consideredcold-formable can be formed by the sonic technique. (This effect wasdemonstrated, for example, in the cold-heading of titanium alloy rivets,in a recent project.)

The basic sonic cold forming process is equally applicable to rollingand shaping of ingots, billets, bars, tubes, pipe, rails, beams, and allother longitudinal shapes produced in primary steel manufacture. Inaddition, the process can be applied to rolling of sheets, plates, barsand other shapes; the process can be used in later finishing, bending,forming, and manufacturing processes by customers of primary steelproducing plants. Stress in a material is defined as applied force overcross-sectional area (F /A). To deform a material the stress which mustbe exceeded is the elastic limit of the material (L For eachapplication, the sonic power input must meet the requirement ofproviding dynamic longitudinal stresses approaching the elastic limitfor the cross-sections and material characteristics involved. To a firstapproximation, the vibratory force required (F) would be nearly equal tothe product of the material cross-section involved (A) and the elasticlimit (L of the workpiece because the required stress to match theelastic limit (L is thus, the required dynamic force would approximateF=AL to provide maximum reduction in the static guiding forces requiredto control the deformation processes. High-power sonic transducers, orseveral lower-power transducers, might be used to excite the workmaterial, when large cross-section work pieces are to be formed.

In bending of shapes, such as bars, rails, plate, sheets, etc., theouter fibers are elongated by tension deformation, and the inner radiusfibers are subject to compression. Fortunately, the alternating stressesproduced by the sonic vibration can aid both deformation processes tooccur simultaneously, as shown in FIGS. 3b and 30.

In present cold rolling and deformation processing, it is frequentlynecessary to remove work materials from the process after certain levelsof deformation, and to anneal or otherwise remove the effects of coldWorking before further processing. This is done because materials areWork-hardened, and build up high levels of internal shear strain energy.Annealing restores ductility to the work material so that it can befurther deformed without producing cracks and fractures. In the sonicprocess, a degree of stress relief occurs due to the rapidly-reversedstresses to which the material is subject (beyond and after thedeformation). This, in turn, aids in retaining the ductilecharacteristics of the work material, and permtis greater deformationsto occur without achieving high levels of work hardening.

The tremendous economic advantage of sonic cold forming lies in theenormous potential reduction in the size, weight, costs, and slowness ofoperation of massive machines which produce cold deformation entirely byapplication of static forces. Generically, the required static forcescan be reduced by ratios of 10:1 up to :1 or more. Since the size andweight (and cost) of machines are proportional to the static forces theymust withstand, sonic excitation can reduce these factors by comparableratios (greatly reducing the capital and amortization costs of suchequipment in industry). Alternatively, the capacities (workcross-sections which can be handled) of exist ing sizes of cold formingand rolling machines might be increased by comparable ratios. Withsmaller machines to do the work, higher operating speeds could also beattained, with additional economic advantages.

What is claimed is:

1. A process for the cold-forming elongation of metals, alloys, andother plastically-deformable materials comprising the steps of applyingvibratory-mechanical energy to the work material in a direction parallelto the direction of elongation of said work material and applying staticforce to said work material at a point other than the point ofapplication of said vibratory-mechanical energy.

2. A process as described in claim 1 further including transmittingreversed dynamic stresses through the work material by applying saidvibratory-mechanical energy to said work material.

3. A process as described in claim 2 wherein said process furtherincludes maintaining the amplitude of said reversed dynamic stresses ata value less than the elastic limit of said work material between thepoint of application of said vibratory-mechanical energy and said staticforce thereby permitting the efiicient transmission of said reverseddynamic stresses between said point of application of saidvibratory-mechanical energy and said static force.

4. A process as described in claim 2 wherein said process furthercomprises combining said reversed dynamic stresses with the staticstresses in said work material thereby creating static stresses byapplying said static force to said work material.

5. A process as described in claim 4 wherein said process furthercomprises varying said static force thereby creating varying staticstresses in said work material.

6. A process as described in claim 4 wherein said process furthercomprises cold-forming said work material when said reversed dynamicstresses in said work material in combination with said static stressesexceed the elastic limit of said work material.

7. A process as described in claim 6 wherein said process furthercomprises cold-forming said work material incrementally once each cycleof said reversed dynamic stress during the period when said combinationof said static stresses with said reversed dynamic stresses exceed saidelastic limit of said work material.

8. A process as described in claim 7 wherein said process furthercomprises combining said reversed dynamic stresses with tensile staticstresses thereby coldforming said work material incrementally byperiodically exceeding the tensile elastic limit.

9. A process as described in claim 7 wherein said process furthercomprises combining said reversed dynamic stresses with compressivestatic stresses thereby cold-forming said work material incrementally byperiodically exceeding the compressive elastic limit.

10. A process as described in claim 7 wherein said process furthercomprises combining said reversed dynamic stresses with tensile staticstresses and compressive static stresses, respectively, wherever saidtensile stresses and compressive stresses exist in said work materialthere by cold-forming said work material incrementally by periodicallyexceeding said tensile and compressive elastic limits, respectively.

11. A process as described in claim 2 wherein said process furthercomprises stress relieving said work material a said work material isincrementally cold-formed wherein the rapidity with which said reverseddynamic stress occurs creates intervals of released stress therebyrelieving shear strain energy, preventing said shear strain energy frombeing stored in said work material as the incremental deformations addup to the total deformation.

12. A process as described in claim 4 wherein said processfurthercomprises cold-forming said work material by applying staticforces more than 10 times less than those required without theassisatnce of said vibratory-mechanical energy.

13. A process as described in claim 4 wherein said process furthercomprises stress relieving said cold-formed work material by saidreversed dynamic stresses created by said vibratory-mechanical energyremaining in said work material after said work material has beencoldformed by said combination of reversed dynamic stresses and saidstatic stresses.

14. A combination for the cold-forming elongation of metal comprising:means for applying static forces to deform the work material, means forsupporting and guiding said work material through said deforming forces,a source of electromechanical energy and means for coupling said sourceof electromechanical energy to said work material at a point parallel tothe direction of elongation of said work material prior to saiddeforming means.

15. A combination as set forth in claim 14 wherein said source ofelectromechanical energy is high power electromechanical sonictransducer.

16. A combination as-set forth in claim 14 wherein said means forcoupling and said source of electromechanical energy further comprisesan electromechanical transducer threaded at its tip and said workmaterial threaded at one end, said threaded portions being joined.

17. A combination as set forth in claim 16 wherein said means forcoupling said work material to said electromechanical transducer furtherincludes intermittent contact means.

I References Cited UNITED STATES PATENTS

